The Worst Company For Women Is Run By....

In recent years, women have made some high-profile jumps to the tippiest-top of the corporate ladder, from Ginni Rometty at IBM to Marissa Mayer at Yahoo. But according to a new report, the overall picture is still bleak for women and minorities. At over half of the country's largest corporations, the highest-paid executive positions are filled exclusively by white men.

Calvert Investments analyzed the diversity of the S&P 100, 100 of the country's major corporations. And the report published Thursday by the investment management firm found that the pipeline to the top isn't just leaky for women, but full of gaping holes. While women are hired about as much as men, they make up just 8 percent of the highest-paid executives.The report ranked the S&P 100 according to various criteria, including their diversity at the top level and their diversity programs.

At the very bottom: Warren Buffett's firm

With just 5 points out of 100, Warren Buffett's multinational conglomerate, Berkshire Hathaway came in dead last. It may be the first time that investing legend Buffett (pictured above) has come at the wrong end of any business list. And it's not that Buffett is unaware that women have long been excluded from his industry. He once famously remarked that he was "privileged to work during a period when it was only necessary to compete against half of the population."

It's ironic that eBay ranks so poorly since Meg Whitman's 10-year tenure as eBay's CEO has been seen as a landmark for women.

At the other end of the spectrum, the report spotlighted Citigroup Inc., Merck & Co., Coca-Cola Co. and JPMorgan Chase for their commitment to diversity.

CEOs try to keep their numbers secret

While most of the top companies had diversity programs, the report found that these don't seem to translate into promotions. But it's hard to tell. Under the Civil Rights Act of 1964, companies must submit the demographic data of their employees to the federal government. But only seven of the 100 companies let the public take a full peek.

In fact, companies are getting even more secretive with their data. Thirty-nine of the companies didn't release any of their demographics to the public at all. When CNNMoney asked the 20 leading tech companies for their diversity data, just two of them -- Dell and Intel -- agreed.

You can't hide a lack of diversity at the very top

White men, who make up just 38 percent of the population, run 91 percent of the S&P 100. (Energy companies appear to be the least welcoming of high-powered women.) But PepsiCo is the clear standout: Among the top five highest-paid executives is just one white man and a CEO who is both female and Indian-American.

Women and minorities are making better gains in the boardroom

Ninety-eight of the companies have at least one woman on their board of directors, and 86 percent have at least one member of a minority group. And at 71 percent of these companies, these women and minorities aren't so lonely -- with at least two other women or minority members at the table too.

Last year, the European Union adopted a proposal to require 40 percent of company board members to be female by 2020. But as the Calvert report shows, the U.S. would be unlikely to meet that standard. Over half of S&P companies don't even say that they look for diversity in their boards. Some are even hostile to the idea.

Berkshire Hathaway has stated: "Berkshire does not have a policy regarding the consideration of diversity in identifying nominees for director. In identifying director nominees, the Governance Committee does not seek diversity, however defined."

This might be a clue as to why the company scored so miserably on a diversity list.